The embodiments described herein relate generally to noise control and more particularly, to improving efficiency and reducing noise generated by a centrifugal fan system using active noise control and anti-noise.
There are many known noise cancellation systems used to cancel unwanted noise in a particular system. For example, there are both passive and active noise control systems. Some known passive noise reduction systems block the noise compression wave with a sound absorbing substance. This type of noise reduction does not require an external energy source to accomplish its task. Some known types of passive noise reduction include sound mufflers, enclosures, and acoustical material. Passive noise reduction tends to be more effective for high frequency noise than for low frequency noise.
Active noise control (ANC) systems are used to electronically sense and cancel undesired noise from noise producing sources such as fans, blowers, electronic transformers, engines, etc. In some known ANC systems, a sensor (such as a microphone) and an actuator (such as a speaker) are located along the same plane as the noise wave-front plane. Some known ANC systems for heating, ventilating, and air conditioning (HVAC) systems consist of a speaker that injects pressure waves (or “anti-noise”) into the ductwork. The pressure waves are generally out-of-phase with the noise to facilitate canceling the noise proximate the speaker. Some of these known systems also include an error microphone to sense the amount of noise cancellation. Feedback signals from the error microphone are then transmitted to ANC control circuitry to provide a drive signal to drive the speaker to minimize the error noise signal. Active noise reduction tends to be more effective for low frequency noise than for high frequency noise.
These known noise control systems include limitations in the noise frequencies in which they are most effective, and can be labor-intensive and expensive to install due to the use of many additional components, such as, actuators, acoustic materials, etc. Furthermore, in such known systems, it is noted that the mechanical or electromechanical actuators themselves can produce unwanted noise. These known systems fail to disclose a complete solution for effective control of noise across a broad frequency range, such as that generated in an HVAC system.